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RobotLocomotion / drake

Model-based design and verification for robotics.
https://drake.mit.edu
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Can't programmatically alter transparency of model loaded from URDF/SDF in visualization #13126

Closed SeanCurtis-TRI closed 4 years ago

SeanCurtis-TRI commented 4 years ago

A user requested the ability to visualize a robot with transparency. The robot is specified in a URDF/SDF file, which in turn references objs and mtl files. The challenge, is that the user wants to apply transparency on top of those specifications. In other words, they shouldn't have to change the specification on disk to achieve a run-time effect.

The relationship between IllustrationProperties and drake_visualizer is such that if the ("phong", "diffuse") value has a non-unit alpha channel, that alpha value will still affect the visualization of the robot whose visual appearance would otherwise be defined by the mtl file. This provides the means.

The missing piece is that SceneGraph::AssignRole() isn't implemented for IllustrationProperty and RoleAssign.kReplace so the diffuse value cannot be changed after parsing. We need to implement this in order to enable this behavior.

SeanCurtis-TRI commented 4 years ago

There's a reason it hasn't been implemented yet. It's discussed in this TODO:

https://github.com/RobotLocomotion/drake/blob/master/geometry/geometry_state.cc#L784-L789

tl;dr Changing the illustration properties does not guarantee that illustration engines will reload their geometry. So, if the load message has already been sent to drake visualizer and then illustration properties are sent, no visible difference will appear.

The short-term solution is to simply document this and put the burden on the caller to make sure they make changes to illustration properties before they connect visualizers.

mposa commented 4 years ago

As the user above, I approve this feature request!

This also seems relevant for https://github.com/RobotLocomotion/drake/issues/9728